The present invention relates to a method and apparatus for cementing a femoral stem hip prosthesis in a femoral canal with the use of a cement.
It is well known in the prior art to initiate total hip replacement as disclosed in U.S. Pat. No. 4,357,716, issued Nov. 9, 1982. In such cases, the femur is prepared to receive a femoral stem prosthesis which has a head, neck and stem. The proximal end of the femur is prepared by resecting the head and neck of the femur and then rasping or curetting the intramedullary canal in its proximal end and extending this process laterally and distally in the proximal shaft of the femur to accommodate a cement mass for support and fixation of the stem of a femoral prosthesis. Once the canal has been properly prepared by reaming and curettage, the distal canal is plugged, utilizing a bone plug obtained from the femoral head or formed in any other of the well known alternate methods. In any case, the plug effectively seals off the canal to prevent excessive penetration of cement below the tip of the stem of the prosthesis. Positioning of the prosthesis stem in the femoral canal and the relationship of the head and neck of the prosthesis with the shaft of the femur is important and is related in part to the position of the distal end of the femoral stem as well as the position of the proximal end of the prosthesis stem in the intertrochanteric area.
As described in U.S. Pat. No. 4,357,716, a fixed jig holds the prosthesis in fixed relationship to the femur thus eliminating motion of the prosthesis during the time that the pressurized cement is applied about the prosthesis stem in the femoral canal and the pressure is maintained until the cement hardens.
It has been found in all prior art methods of inserting the prosthesis stem in the femoral canal that, because there are such a variable number, shapes and sizes of femoral stems, it is difficult to place the trial femoral stem prosthesis into the femoral canal unless the distal tip of the prosthesis stem touches the cortical bone anteriorly or posteriorly and in a few instances perhaps medially or laterally. The touching of the cortical bone by the distal end of the stem is believed to be detrimental, however, inasmuch as it creates a pressure point on the cortical bone structure which may cause bone failure when the weight distribution of the patient is applied to the head of the femoral stem prosthesis and the weight transferred to the stem. These pressure points may either cause failure of the cortical bone or loosening of the cement holding the prosthesis stem in the femoral canal thereby creating problems for the patient. The cement should encircle the entire stem rather than having little or no cement at the tip of the prosthesis stem. However, this cannot be determined in the prior art prior to the cementing of the prosthesis stem in the canal itself. After the cementing has taken place in the prior art, the device can be x-rayed and the position of the stem determined with respect to the cortical bone structure of the femur. In such case, however, it is then too late to reposition the stem in a more desirable position.
Thus, it is an object of the present invention to correctly position the prosthesis in the femoral canal prior to cementing said stem in said canal such that a spacing exists everywhere between the stem of the prosthesis and the cortical bone of the femur and after this correct position has been determined, then the space between the stem and the cortical bone is filled with cement to hold the prosthesis in the femoral canal. It is also an object of the present invention to determine the correct spaced position of said stem in said canal prior to filling the space with the cement.
It is still another object of the present invention to support the prosthesis in the correct spaced position during filling of the space with cement and while the cement hardens.
It is yet another object of the present invention to place a spacing sleeve over the stem of the prosthesis and insert the prosthesis stem in the femoral canal with the sleeve holding the stem in the desired spaced relationship with the canal cortical bone.
It is another object of the present invention to attach a guide to the femur to support the prosthesis stem in its correct spaced position in the canal and then removing the stem from the canal whereby the spacing sleeve may be removed and the stem reinserted in said canal and held by said guide in its predetermined correct spaced position with the cortical bone.
It is still another object of the present invention to form the spacing sleeve of a cement permeable material whereby the stem is held in spaced relationship with the cortical bone of the femoral canal, said cement permeable material allowing flowable cement to pass therethrough and substantially surround the stem and contact substantially all of the cortical bone.